1. Field of the Invention
The present invention relates to a mobile communication system, a radio base station, a scheduling apparatus, a scheduling method employed in the same and a program thereof, and more particularly to a packet scheduling method of the radio base station in the mobile communication system which performs packet communication.
2. Description of the Prior Art
In recent years, in a mobile communication system, as data communication such as Internet browsing and electronic mail including images (still image and moving image) increases, the demand for data communication is on the rise. In W-CDMA (Wideband Code Division Multiple Access) as the third-generation mobile communication system, the standardization of HSDPA (High Speed Downlink Packet Access) which implements high-speed downlink packet communication is under way by 3GPP (3rd Generation Partnership Project).
In the HSDPA, which implements high-speed packet communication in downlink shared channel, since a radio base station assigns a transmission opportunity to a plurality of mobile stations in accordance with downlink radio channel quality, the throughput can be improved by user multiplex effect. The method of assigning a transmission opportunity is termed a scheduling. The following methods are known as representative ones.
Max. C/I [Maximum CIR (Carrier to Interference power Ratio)] method (for example, refer to non-patent document 1) assigns a slot to a mobile station in which the radio channel quality is highest with respect to mobile stations in a waiting state for transmitting a packet. In this method, the throughput performance can be considerably increased. However, the frequency of assigning a transmission opportunity to a mobile station in which the radio channel quality is not satisfactory because it is located at places such as the boundary of a cell, may be reduced.
PF (Proportional Fairness) method (for example, refer to non-patent document 2) is a scheduling method which aims at fairly assigning a transmission opportunity to a mobile station in a waiting state for transmitting a packet. In this method, for example, “instantaneous radio channel quality/average radio channel quality” of mobile stations is determined as a metric so as to assign a transmission opportunity to a mobile station in which the metric is large.
According to the PF method, since relative quality with respect to average radio channel-quality is employed as an indicator, it is possible to assign a transmission opportunity even to a mobile station in which the average radio channel quality is low.
(Non-patent document 1) 3GPP TR25.848 V.4.0.0 (2001-03), “Physical layer aspects of UTRA High Speed Downlink Packet Access”, pp. 69-70, A.3.5 Packet scheduler
(Non-patent document 2) A. Jalali et al., “Data Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal Communication Wireless System”, IEEE 51st Vehicular Technology Conference (2000)
In the conventional scheduling methods, however, while the radio channel quality of a mobile station is taken into consideration to improve the throughput, quality guarantee for each service is not considered, when a transmission opportunity is assigned to the mobile station.
In the future communication service, when the quality guarantee for each service is needed, the service quality (QoS: Quality of Service) may not be satisfied. According to the PF method, if a ratio of a measured transmission rate to a predetermined transmission rate is employed as a metric, the service quality can be satisfied, for example.
In this case, however, since the condition for assigning a transmission opportunity does not take the radio channel quality into consideration, a transmission opportunity is assigned even when the radio channel quality is low, thereby reducing the throughput. Consequently, in the conventional scheduling methods, it is difficult to simultaneously achieve the service quality guarantee and the improvement of throughput.